A. Field of the Invention
This invention relates to a micromeasuring device capable of measuring very small dimensions of the order of 1 micron or less, and capable of checking whether the tolerance of mechanical components has or has not been exceeded in relation to nominal dimensions. The apparatus according to the invention can also be used for positioning a mechanical component according to the position of a control component with a predetermined tolerance.
B. Description of the Prior Art
Apparatuses for detecting the movement of a movable indicating element of a measuring instrument past a predetermined limit position are known in the prior art and, for example, disclosed in British Pat. No. 1,449,776 of Sept. 18, 1974. Such apparatus includes a detection head incorporating two photoelectric receivers for receiving light transmitted, reflected or emitted thereto by the indicating element, the photoelectric receivers being spaced apart in the direction of movement of the indicating element for positioning one on each side of a position corresponding to the predetermined limit position so that, as the indicating element passes the limit position, the photoelectric receivers are consecutively subjected to a change in the light received from the indicating element resulting in differential illumination of the photoelectric receivers; and an electronic circuit which is connected to receive the output signals of the photoelectric receivers and is operative to deliver a detection signal for actuating a signalling device when the movable element passes its limit position in one direction and to cease delivering the detection signal when the movable element moves back past the limit position in the other direction.
Advantageously, the electronic circuit of this prior art apparatus includes a bistable stage so coupled to the photoelectric receivers that, when the indicating element moves past the detection head in the said one direction, the bistable stage is brought from a normal state into an operative state in which it delivers the said detection signal, the bistable stage returning to its normal state only when the indicating element moves back past the detection head in the said other direction. Preferably, the two photoelectric receivers and their load resistors are connected in series between power supply terminals of the electronic circuit and the common point of the two photoelectric receivers is so connected to the input of the bistable stage that the changeover thereof into its operative state occurs only when the indicating element moves in the said one direction past both photoelectric receivers and the return of the bistable stage to its normal state occurs only when the indicating element moves back in the said other direction past both of the photoelectric receivers.